Nutrition response of Norway spruce and willow to varying levels of calcium and aluminium

Abstract

Decreased forest tree growth has often been attributed to increasing soil acidification, especially from high concentrations of soluble Al³⁺ and low base saturation. The growth of willow cuttings (Salix viminalis L. 78183) and Norway spruce seedlings (Picea abies L. Karst) were measured in a greenhouse in the presence of variable Ca²⁺ at uniform NH ⁺₄ concentrations. Sets of willows were grown in sand culture, one watered with Ingestad's nutrient solution (INS, pH 5.4) and the other watered with acidified Ingestad's nutrient solution (NSA, pH 3.8). Three levels of Ca²⁺ and Al³⁺ concentrations (in NSA only) were established for all nutrient solutions. Sets of Norway spruce seedlings were grown in calcareous sand and watered with INS, one of pH 5.4 and the other of pH 2.1 (resulting in two Ca²⁺ concentrations after acid neutralization by CaCO₃). In the field, observations were made on the correlation of naturally occurring soil solution Al³⁺ and Ca²⁺ to spruce needle Al, Ca²⁺ and N concentrations. In the willow studies, both the above- and below-ground biomass were negatively influenced by the presence of Al³⁺. Aluminium decreased the growth of rooted cuttings (more in roots than shoots), reduced the uptake of N, Ca²⁺, Mg²⁺ and P, significantly lowered the weight of fine roots, and caused overall reductions of tissue nutrient concentrations. As Al³⁺ concentrations increased, increased concentrations of Ca²⁺ were needed by the willow to help ameliorate the effects of Al³⁺. In field samples of spruce needles and soil, CAB (CAB = Log₁₀ Ca²⁺ /Al³⁺) was positively correlated with N concentration. From a combination of greenhouse and field studies the mechanisms for Ca²⁺ amelioration of Al³⁺ toxicity in trees appear to be i) the effect of Ca²⁺ on reduced absorption of Mn²⁺ and Al³⁺, ii) the effects of Ca²⁺ on NH ⁺₄ and P absorption, iii) and the stimulation of tree growth.